Rotary viscosimeter

A rotary viscosimeter which has a rotary measuring cylinder that is disposed in a cylindrical measuring cup holding the sample to be tested in a measuring gap formed between the cylinder and the cylindrical wall of the cup. Forces required to rotate or angularly deflect the cylinder are measured and used to determine the viscosity of the sample. The temperature of the sample in the gap is maintained uniform by constructing the measuring cup of a good heat conducting material and surrounding it with a control cup, also constructed of a good heat conducting material, and the cups are configured to form an isolation gap between them. At least one heat pump in heat conducting contact with an outer surface of the heat control cup controls the heat flow to and from the heat control cup, and a good heat conducting contact area is formed between the cups at the upper ends of the measuring cup to provide a controlled heat flow to or from the measuring cup.